WO2003067579A1

WO2003067579A1 - Optical recording/reproducing method and optical recording medium

Info

Publication number: WO2003067579A1
Application number: PCT/JP2003/000531
Authority: WO
Inventors: Yuichi Sabi; Takashi Iwamura; Mitsuaki Oyamada; Sakuya Tamada
Original assignee: Sony Corporation
Priority date: 2002-01-22
Filing date: 2003-01-22
Publication date: 2003-08-14
Also published as: US20040095867A1; KR100943103B1; KR20040079829A; EP1469460A4; TW200307923A; JPWO2003067579A1; US7092343B2; CN1498399A; CN1266681C; EP1469460A1; TWI225244B; CA2441559A1

Abstract

An optical recording medium having two or more information recording layers in which information is recorded at high recording density. The incidence of light on the information recording layer disposed far from the top layer through which light enters and the returning light from the information recording layer can be detected at high efficiency. The recording/reproducing characteristics are favorable. An optical recording/reproducing method for at least reproducing/recording information from/on this optical recording medium is also disclosed. The optical recording medium (10) comprises information recording layers (21, 22) between a first major surface on which light can be incident and a second major surface opposed to the first major surface. The first information recording layer (21) nearest to the second major surface is a phase-modulation information recording layer, and the second information recording layer (22) is a reflectance-modulation information recording layer. Information is reproduced or recorded from or in the first information recording medium (21) of the optical recording medium (10) by a phase modulation method, and information is reproduced or recorded from or in the second information recording layer (22) by a reflectance modulation method.

Description

Specification

Optical recording / reproducing method and optical recording medium

The present invention relates to an optical recording / reproducing method for at least reproducing or recording information and an optical recording medium. Background art

Higher recording densities in optical recording media, for example, optical discs, are usually realized by a method of shortening the wavelength of irradiation light and increasing the numerical aperture of an objective lens. By combining this with the multi-layered information recording layer, a dramatic increase in density can be realized.

However, in an optical recording medium, when the information recording layers are multi-layered, that is, when a plurality of information recording layers are stacked, the main surface (incident surface) on the light incident side of the optical recording medium due to light absorption in each information recording layer. There is a problem that the farther the information recording layer is from the viewpoint, the lower the amount of light that can reach.

This is an inevitable problem when a single light source is used for a plurality of information recording layers.

The same applies to the return light from the information recording layer, that is, the reproduction detection light. The return light to the information recording layer at a position far from the incident surface is the light of the optical recording medium while the light is being detected. Since the light passes through the other information recording layer located on the incident surface side and returns, the amount of light decreases.

Therefore, it is necessary to set the reflectance higher for an information recording layer farther from the incident surface. At the same time, the degree of modulation needs to be as high as possible. By the way, the principle of detecting an optical recording medium, for example, an optical disk can be roughly classified into two types.

One is the phase modulation method represented by the so-called CD-R or DVD-R of a CD-ROM (Compact Disc-Read Only Memory) disk, a write-once CD or DVD (Digital Versatile Disc). It is.

In this phase modulation method, while the reflectance in an information recording mark and the reflectance in the vicinity thereof are made equal to make the reflectance constant, the optical path length in the information recording mark and the optical path length in the vicinity are determined. By making them different, the phase of the reflected light changes, causing interference in the light spot, and as a result, the amount of return light changes.

The other is a reflectivity modulation method represented by an optical disk using a phase-change material such as a rewritable CD or DVD, that is, a so-called CD-RW or DVD-RW. In this reflectance modulation method, a change in the amount of return light due to a difference in reflectance is directly detected by utilizing the fact that the reflectance in an information recording mark is lower than the surrounding reflectance.

By the way, the information holding layer, that is, the information recording layer in the phase modulation method represented by the above-mentioned CDR and DVDR is generally constituted by a recording film made of an organic dye. As described above, the optical recording medium in which the recording film is made of the organic dye material has advantages such as easy production, easy handling of the material, and low cost.

In this phase modulation method, the reflectance is maintained almost constant without changing before and after recording, which causes effective interference between the information recording mark and its surroundings. Is needed.

For this reason, in the case of a CD-R or the like, a thick Au is required for the information recording layer composed of the recording film composed of the organic dye. Alternatively, the structure is such that a metal film of Ag or the like is laminated so that the reflectance does not change before and after recording.

However, applying a structure in which a metal film having a large thickness is laminated on an information recording layer to multi-layer the information recording layer as described above requires an information recording layer far from the incident surface to be applied to the information recording layer. There is a problem that the incident light cannot reach.

Therefore, such a conventional design of a recording film made of an organic dye cannot be directly applied to a multilayer information recording layer. Disclosure of the invention

The present invention relates to an optical recording / reproducing method for at least reproducing / recording information on an optical recording medium and the recording medium, wherein the configuration of the optical recording medium is such that two or more information recording layers are laminated. An optical recording medium having a multi-layered structure, capable of detecting light incident and returned light with high efficiency on an information recording layer located far from the incident side of the optical recording medium.

Further, in the present invention, the multilayer information recording layer of the optical recording medium can be constituted by a recording film made of an organic dye, thereby simplifying the production and reducing the price. It is an object of the present invention to provide an optical recording medium and an optical recording / reproducing method capable of obtaining good recording / reproducing characteristics for an information recording layer.

The optical recording / reproducing method of the present invention is a method for reproducing or recording at least information on an optical recording medium, and as the optical recording medium, one main surface on the light incident side of the optical recording medium; It has a plurality of information recording layers between it and the other main surface on the opposite side, and the first information recording layer closest to the other main surface is the phase modulation type information recording layer, Using an optical recording medium in which the recording layer is a reflectance modulation type information recording layer, the first information recording layer is phase-modulated by light incident from one main surface side. In this case, information is reproduced or recorded in accordance with the method described above, and information is reproduced or recorded in the other information recording layer in accordance with the reflectance modulation method.

The optical recording medium of the present invention has one main surface through which light can enter, and a plurality of information recording layers between the other main surface opposite to the one main surface, The first information recording layer closest to the other main surface is a phase modulation type information recording layer, and the other information recording layer is a reflectance modulation type information recording layer.

Further, in the optical recording medium used in the optical recording / reproducing method of the present invention described above, and in the optical recording medium of the present invention described above, at least one information recording layer of a plurality of information recording layers has physical properties by light absorption. A structure containing an organic material that causes a change to cause a change in an optical constant can be provided, and an organic dye can be used as the organic material.

According to the optical recording / reproducing method of the present invention described above, a plurality of information recording layers are provided between one main surface on the light incident side and the other main surface on the opposite side, and the other main surface has Using an optical recording medium in which the near first information recording layer is a phase modulation type information recording layer and the other information recording layer is a reflectance modulation type information recording layer, light incidence from one principal surface side By reproducing or recording information on the first information recording layer by a phase modulation method, and by reproducing or recording information on another information recording layer by a reflectance modulation method, It is possible to reproduce and record information on a plurality of information recording layers of the optical recording medium by irradiating light from one main surface side of the recording medium.

According to the configuration of the optical recording medium of the present invention described above, the first information recording layer closest to the other main surface is a phase modulation type information recording layer. Signal detection can be performed by a phase modulation method. Further, since the other information recording layer is a reflectance modulation type information recording layer, signal detection can be performed by a reflectance modulation method. . In the optical recording medium used in the optical recording / reproducing method according to the present invention,

In the case where the first information recording layer and the other information recording layer are formed of an organic dye film, the principle of recording is to cause a change in the refractive index before and after recording. In other words, for example, the refractive index of the organic dye film before recording is set so as to be significantly different from the refractive index of the adjacent layer, for example, the substrate, and the reflection at the interface between the organic dye film and another material layer in contact with the organic dye film. At the same time, the refractive index of the organic dye film after recording is set to be close to the refractive index of the other material layer forming the above-described interface, and the interface between the organic dye film and the substrate is set. By reducing the reflectance in the above, it is possible to detect a recording information signal as a so-called reflectance modulation type information recording layer that directly detects the reflectance.

On the other hand, the phase modulation type information recording layer can be formed by changing the optical path length by recording by such a change in the refractive index.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic configuration diagram (cross-sectional view) of an optical disc according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of the optical disc having three information recording layers. FIG. 3 is a schematic configuration diagram of an embodiment of an optical pickup for reproducing and recording information with respect to the optical disc of FIG. 1, and FIGS. 4A and 4B show the width of the guide groove of the information recording layer. FIG. 9 is a diagram showing the result of measuring the modulation factor while changing. BEST MODE FOR CARRYING OUT THE INVENTION

The present invention relates to a method for at least reproducing or recording information on an optical recording medium, wherein the optical recording medium has one main surface on a light incident side with respect to the optical recording medium and another main surface on the opposite side. A plurality of information recording layers between the main surface and the first information recording layer closest to the other main surface. Using an optical recording medium with a phase modulation type information recording layer and another information recording layer with a reflectance modulation type information recording layer, the first information recording layer Is an optical recording / reproducing method in which information is reproduced or recorded by a phase modulation method, and information is reproduced or recorded in another information recording layer by a reflectance modulation method.

The present invention also provides the optical recording / reproducing method, wherein

In the information recording layer of No. 1, the reflectance before recording at the position corresponding to the information recording mark is R. Assuming that the reflectance after recording at the same position is R, the rate of change (R. — R) ZR. Is smaller than the modulation degree of the reproduction detection signal of the information recording mark, and the other information recording layer has the same rate of change of the information recording mark (R _D -R) ZR. Is equal to or greater than the modulation degree of the reproduction detection signal of the information recording mark.

The present invention has one main surface through which light can enter, and a plurality of information recording layers between the other main surface opposite to the one main surface. The first information recording layer closest to the optical recording medium is a phase modulation type information recording layer, and the other information recording layer is a reflectance modulation type information recording layer.

Further, the present invention provides the optical recording medium, wherein the width of the recording area of the reflectance modulation type information recording layer is wider than the width of the recording area of the phase modulation type information recording layer.

The present invention also provides the optical recording medium, wherein the first information recording layer has a reflectance before recording at a position corresponding to an information recording mark. Assuming that the reflectance after recording at the same position is R, the rate of change (R.I.R) ZR. Is smaller than the modulation degree of the reproduction detection signal of the information recording mark, and the other information recording layers have the same rate of change of the information recording mark (R.-R

) Z R. Is set to be equal to or higher than the modulation degree of the reproduction detection signal of the information recording mark.

Further, the present invention provides the optical recording medium, wherein a plurality of information recording layers are provided. At least one or more of the information recording layers is formed of a recording film whose optical constant changes due to light absorption.

Further, the present invention provides the above-mentioned optical recording medium, wherein the recording film further contains an organic material which causes a change in physical properties due to light absorption to cause a change in an optical constant.

Further, the present invention is configured such that in the optical recording medium, an organic dye is further used as an organic material.

Further, the present invention is configured such that in the optical recording medium, a reflection layer is provided on the other main surface side of the first information recording layer.

FIG. 1 shows a schematic configuration diagram (cross-sectional view) of an optical disk as one embodiment of the present invention.

The optical disc 10 has a reflective layer 12, a first information recording layer 21, an intermediate layer 13, a second information recording layer 22, and a surface protective layer (light transmitting layer) on a substrate 11. 1) and 4 are laminated.

That is, the information recording layer is composed of the first information recording layer 21 and the second information recording layer.

2 2 layers. .

Further, the optical disc 10 of the present embodiment has a configuration in which the light L is incident not from the substrate 11 side but from the side opposite to the substrate 11, that is, from the surface protective layer 14 side.

Guide grooves (not shown) are provided on the substrate 11 and the intermediate layer 13 so that the first information recording layer 21 and the second information recording layer 22 can be tracked, respectively.

As the first information recording layer 21 or the second information recording layer 22, a film that changes the optical constant due to light absorption can be used.

In addition, only one of the first information recording layer 21 and the second information recording layer 22 may be a film that changes the optical constant by light absorption.

The optical constant changes due to light absorption, causing the information recording layer to buckle. The folding ratio changes.

The first information recording layer 21 and the second information recording layer 22 can be formed of an organic material film, for example, an organic dye film.

The organic dye film is made of a material that changes its physical properties by light absorption (for example, the molecular structure changes due to thermal decomposition, or the molecular arrangement changes as it is, or a composite thereof).

As such an organic dye film, a conventionally known material, for example, triphenylamine tetramer or the like can be used.

When the recording film constituting the information recording layer is formed of an organic dye film in this manner, there is an advantage that the production can be simplified and the price can be reduced.

As the reflection layer 12, a film having a high reflectance with respect to the incident light L is formed.

As the reflection layer 12, a metal film, for example, an Ag alloy sputtered film or the like can be used.

For the intermediate layer 13 and the surface protective layer 14, a material having a high transmittance to the incident light L is used. For example, a UV curable resin can be used.

The thickness of the intermediate layer 13 is preferably 5 to 50 μm.

Further, the first information recording layer 21 is a phase modulation type information recording layer capable of reproducing or recording information by a phase modulation method.

Therefore, the reflectance before recording at the position corresponding to the information recording mark before the recording is R. Where R is the reflectance after recording at the same position (R. — R) ZR. The force is formed so as to be smaller than the modulation degree of the reproduction detection signal of the information recording mark.

This makes it possible to detect a signal modulated by the phase modulation method, since the change in reflectance before and after recording is very small. Thus, the first information recording layer 21 can be a phase modulation type information recording layer.

In order to make the change in reflectance before and after recording extremely small, the first information recording layer 21 is provided with the reflection layer 12 on the side opposite to the light incident surface. In addition, the width of the recording area is defined in accordance with the wavelength of the light source of the readout optical system and the numerical aperture NA of the condenser lens so that a signal with a sufficient degree of modulation is obtained and SZN is increased.

As described above, the first information recording layer 21 is provided with the reflection layer 12 made of a material having a relatively high reflectance on the side opposite to the light incident surface. Both the reflectance of the information recording layer 21 before recording and the reflectance after recording are close to the reflectance of the reflection layer 12, and the optical constant between the information recording mark and the information recording layer 21 before recording is low. Since the refractive index is different, the optical path length during the round trip to the reflective layer 12 is different.

This makes it possible to detect a signal modulated by the phase modulation method.

On the other hand, the second information recording layer 22 is a reflectance modulation type information recording layer capable of reproducing or recording information by a reflectance modulation method.

Therefore, the reflectance before recording at the position corresponding to the information recording mark before recording is R. And the reflectance after recording at the same position as R, the rate of change (R.-R) / R. Is formed so as to be equal to or higher than the modulation degree of the reproduction detection signal of the information recording mark.

As a result, since the change in reflectance before and after recording becomes large, it is possible to detect a signal modulated by the reflectance modulation method, and the second information recording layer 22 is used as a reflectance modulation type information recording layer. It can be

And a signal with a sufficient degree of modulation is obtained and SZN becomes high. Thus, in the second information recording layer 22, the width of the recording area is defined in accordance with the wavelength λ of the light source of the readout optical system and the numerical aperture 集光 of the condenser lens.

Therefore, the width of the recording area may be different even if the first information recording layer 21 is formed using the same material.

Further, when the recording films constituting the two information recording layers 21 and 22 are formed of organic dye films, the following operation is performed.

In this case, since the refractive index changes before and after recording, it is possible to detect signals without providing a reflective film to the recording film.o

In other words, the refractive index of the organic dye film before recording is set so as to be significantly different from the refractive index of an adjacent layer, for example, the substrate, so that reflection occurs at the interface between the organic dye film and the substrate, and the recording is performed. The refractive index of the subsequent organic dye film is set so as to be close to the refractive index of the substrate to reduce the reflectance at the interface between the organic dye film and the substrate. This makes it possible to detect the signal.

In this case, since the reflectance is directly detected, the information is reproduced or recorded by the reflectance modulation method.

On the other hand, when the reflective layer 12 is provided on the recording film, the change in the reflectance before and after the recording becomes small, and the above-described change in the refractive index changes the optical path length in the recording film. Changes the phase of light before and after recording. This makes it possible to detect a signal by using the interference of return lights having different phases.

In this case, the information is reproduced or recorded by the phase modulation method. Therefore, when the recording film constituting the information recording layers 21 and 22 is formed by the organic dye film, the phase modulation depends on the presence or absence of the reflection layer 12. Reproduction or recording of information by either It can also be configured to perform.

In the first information recording layer 21 and the second information recording layer 22, the recording area has two surfaces having a step formed by the guide groove therebetween, that is, a surface close to the light incident side (lane). And the surface farther from the light incident side (groove) may be provided on either surface.

Regardless of whether the recording area is provided in the land section or the group section, reflection is performed in accordance with the spot size of the incident light L (wavelength of the light source; determined according to I and the numerical aperture NA of the objective lens). The width of the recording area is adjusted so that a sufficient degree of modulation can be obtained by the rate modulation method or the phase modulation method, and the information can be reproduced or recorded on the information recording layers 21 and 22.

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For example, when the wavelength of the light source; l is 405 nm and the numerical aperture NA of the objective lens is 0.85, the width of the recording area must be 0.12 to 0.1 to adopt the reflectance modulation method. It is preferable that the width of the recording area be 0.09 to 0.22 m in order to adopt the phase modulation method.

If the wavelength of the light source is, for example, in the range of 360 to 460 nm, the wavelength becomes shorter than that of a normal optical disc such as a CD-R, so that the size of the optical spot is reduced. Thus, the recording density of the optical recording medium can be improved.

The first information recording layer 21 and the second information recording layer 22 can perform reproduction and recording with the same optical head.

Using an optical pickup with an optical head for reproducing and recording on an optical disc with one information recording layer composed of an organic dye film, the optical disc for focusing (focusing) can be used, for example. The light spot caused by the incident light L is moved between the first information recording layer 21 and the second information recording layer 22 by moving in a direction substantially perpendicular to the surface, and the respective information recording layers 21 are moved. Or reproduction of information for 22 And record.

Here, with respect to the first disk 10 of the configuration of the present embodiment described above,

FIG. 3 shows a schematic configuration diagram of an embodiment of an optical pickup for reproducing and recording information.

This optical pick-up consists of a light source 51 and a grating 52

, A polarizing beam splitter (PBS) 53, a quarter-wave plate 54, an objective lens 55, a Wollaston prism 56, and a lens group serving as a condenser lens and a cylindrical lens 5 7 and a photodetector 58. Although not shown, the light source 51 is configured as a unit including a semiconductor laser that emits laser light having a wavelength of, for example, 405 nm, a collimator, and anamorphism. The objective lens 55 is composed of two optical lenses. The light detecting section 58 functions as a sub-body detector and an RF detector.

With the optical pickup having such a configuration, even if the optical disk 40 is the optical disk 10 of the above-described embodiment, the optical disk has only one information recording layer made of an organic dye. Even so, it is possible to reproduce and record information.

According to the above-described embodiment, the reflection layer 12 is provided adjacent to the first information recording layer 21, and the reflectance is increased by the reflection layer 12, so that the first information recording layer 2 The signal intensity from 1 can be increased, and the change in reflectance before and after recording can be reduced.

Then, the change rate of the reflectance before and after recording at the position corresponding to the information recording mark (R.I.R) / R. Is smaller than the modulation degree of the information recording mark reproduction detection signal, so that the phase modulation method can be used for reproducing and recording information on the first information recording layer 21 o

On the other hand, since the second information recording layer 22 does not have a reflective layer, the transmittance of the second information recording layer 22 is increased so that a sufficient amount of light can be obtained. 1 information recording layer 2 1.

Also, the rate of change of the reflectance before and after recording at a position corresponding to the information recording mark (R _Q -R) / R. Is larger than the modulation degree of the reproduction detection signal of the information recording mark, it is possible to employ the reflectance modulation method for reproducing and recording information on the second information recording layer 22.

This makes it possible to realize an optical disc 10 having two or more information recording layers 21 and 22 while using, for example, an organic dye as a material for the information recording layer.

Then, by forming the information recording layers 21 and 22 in multiple layers, the recording density of the optical disk 10 is dramatically increased.

In addition, when the organic dye is used as a material of the information recording layer, that is, when the recording film constituting the information recording layer is formed of the organic dye film, further simplification of manufacturing and cost reduction are achieved. The cost can be reduced.

Note that a dielectric protection film may be formed between each of the information recording layers 21 and 22 and the intermediate layer 13 or between the second information recording layer 22 and the surface protection layer 14.

Next, an optical disk having the configuration of the above-described embodiment was actually manufactured and its characteristics were examined.

(Example 1)

An optical system was constructed using a blue LD, ie, a semiconductor laser diode (emission wavelength: 405 nm) with a luminescent color, and a numerical aperture (NA) of 0.85 as the light source. .

Then, the structure of each layer of the optical disk 10 was optimized for this optical system.

That is, each layer of the optical disc 10 had the following configuration.

Substrate 11: Polycarbonate resin Reflective layer 1 2: Sputtered Ag alloy film 30 nm

First information recording layer 21: Organic dye film (triphenylamine tetramer) 40 nm

Middle layer 13: UV cured resin 30 m

Second information recording layer 22: Organic dye film (triphenylamine tetramer) 40 nm

Surface protective layer 14: UV cured resin 8 Qm

Since the thickness of the intermediate layer 13 is desirably 15 βm or more in order to suppress the crosstalk between the first information recording layer 21 and the second information recording layer 22, the thickness is 30 μm. m.

The first information recording layer 21 and the second information recording layer 22 each include a triphenylamine tetramer, more specifically, N, N'-bis (4-diphenylamino- 4-biphenyl). N, N'-diphenylbenzidine 6-4) is used. O Hereinafter, it is abbreviated as triphenylamine.

At the wavelength of the light source of 450 nm, the refractive index of triphenylamine is 2.31, and the absorption coefficient is 0.13. The refractive index after recording is 2.1.

This triphenylamine can be formed by vapor deposition.

O

The intermediate layer 13 and the surface protective layer 14 were made of a UV-curable resin with the trade name SD-301, but other materials, a method using a UV-curable adhesive, It is also possible to form with a combination of one sheet and adhesive.

Further, the material of the reflective layer 12 may be any material as long as the readout optical system has a sufficiently high reflectance at the wavelength of the light source. The base material It is also possible to use.

Further, for the first and second information recording layers 21 and 22, it is also possible to use another organic dye material optimized when using a blue LD as a light source. If there is another material capable of spin-coat sputtering, the information recording layer may be formed by spin coating or sputtering.

Using each of the above-described materials, an optical disk 10 having the configuration shown in FIG. 1 was manufactured as follows.

First, a substrate 11 made of a polycarbonate material having guide grooves (for the first information recording layer 21) formed by an injection method is removed.

Next, an Ag alloy film was formed on the substrate 11 by sputtering to form a reflective layer 12.

Subsequently, a first information recording layer 21 was formed on the reflective layer 12 by forming a film of triphenylamine by vapor deposition.

Next, an intermediate layer 13 made of a UV-curable resin was formed on the first information recording layer 21.

Further, a stamper having a shape of a guide groove (for the second information recording layer 22) was pressed against the intermediate layer 13, and the guide groove was transferred by UV curing.

The track pitch of the guide grooves in the guide grooves for the first information recording layer 21 and the guide grooves for the second information recording layer 22 was both 0.32 ^ m. In addition, the depth of each guide groove was set to 2 On m.

In the first information recording layer 21 and the second information recording layer 22, the surface near the light incident side, that is, the land portion, of the step formed by the guide groove was used as a recording area.

The guide groove for the first information recording layer 21 formed on the substrate 11 has a recording area for sufficiently obtaining a detection signal by the phase modulation method. The width of the 531 key, that is, the land portion was set to 0.12 m.

The guide groove for the second information recording layer 22 formed on the intermediate layer 13 is a recording area for performing reproduction or recording on the second information recording layer 22 by a reflectance modulation method. The width of the land portion was 0.16 m, which was wider than the guide groove for the first information recording layer 21.

Subsequently, a second information recording layer 22 was formed on the intermediate layer 13 by forming a film of triphenylamine by vapor deposition.

Then, on the second information recording layer 22, a surface protective layer 14 made of a UV-curable resin was formed, and an optical disc 10 having the configuration shown in FIG. 1 was produced. This was designated as optical disk 10 of Example 1.

(Evaluation)

First, with respect to the optical disc 10 of Example 1, the amount of reflected light was measured while the amount of incident light was kept constant.

As a result, the return light quantity from the second information recording layer 22 was 13%, and the return light quantity from the first information recording layer 21 was 14%. This means that the reflectance when the information recording layer is a single layer of the first information recording layer 21 is 25%, and the light transmittance in the second information recording layer 22 is 74%. Does not contradict.

Although the transmittance in the information recording mark after the recording of the second information recording layer 22 is 78%, the transmittance is averaged to 76% in the entire recording area. The amount of return light from the information recording layer 21 increases, but this is a problem that does not affect the characteristics of a signal obtained by the return light, and thus causes no problem.

Subsequently, a recording / reproducing experiment was performed on the optical disc 10 of the first embodiment.

First, recording was performed on the second information recording layer 22. The recording conditions are as follows. The linear velocity during recording was 5.72 m / s, and the recording pattern was the pattern of a carrier wave with a mark length and space length of 0.69 m. JP03 / 00531 Also, the light intensity at the time of recording was set to 5.0 mW, and the 0.69 m mark was recorded by irradiating it with seven pulses of Duty 50%.

As a result, a rectangular signal with a modulation factor of 40% was obtained.

Here, as described above, the transmittance of the second information recording layer 22 is 7 4

When recording on the first information recording layer 21, it is necessary to increase the amount of incident light in consideration of the loss in the second information recording layer 22. However, there is no problem since other than the incident light amount does not affect the recording characteristics.

Since the optical disc 10 is a write-once type (write-once type), recording is performed before the first information recording layer 21, so that the recording of the first information recording layer 21 is performed. At this time, since the second information recording layer 22 has not been recorded at all, the transmittance is constant and the required recording power hardly varies.

Subsequently, with respect to the optical disc 10 of the first embodiment, recording was performed on the first information recording layer 21, and the first information recording layer 22 was recorded without recording on the first information recording layer 22. The information recording layer 21 was reproduced.

As a result, almost the same signal was obtained as in the case where only the second information recording layer 22 was recorded / reproduced. The degree of modulation was 50%.

That is, it was shown that a similar signal was obtained from the first information recording layer 21 and the second information recording layer 22.

Further, the first information recording layer 21 and the second information recording layer 22 are recorded on the optical disc 10 of Example 1 in this order, and the recording is performed for all the recording errors. After that, the first information recording layer 21 was read.

As a result, the transmittance of the second information recording layer 22 became larger than in the previous case, but the amount of light returned from the first information recording layer 21 was about 15%, and the first information Between recording layer 21 and second information recording layer 22 Since the gap was sufficiently empty, almost no intersymbol interference between the layers was observed, and a signal waveform almost the same as that obtained when recording was performed only on the first information recording layer 21 was obtained.

Thus, it is clear that the recording / reproducing is properly performed on the two information recording layers 21 and 22 in the optical disc 10 of the first embodiment. ·

Accordingly, it was shown that the two information recording layers 21 and 22 can improve the recording density as compared with an optical disc having a single information recording layer.

(Comparative example) ·

On the other hand, as a configuration for comparison, the present invention was not applied, the reflective layer 12 made of a metal film was not provided between the first information recording layer 21 and the substrate 11, and the first information recording was performed. The layer 21 has the same film configuration and guide groove shape (width of recording area of 0.16 m) as the second information recording layer 22, and the other components are the same as those of the optical disc 10 of the first embodiment. As a configuration, an optical disc of a comparative example was manufactured.

In the optical disc of this comparative example, the amount of light detected from the first information recording layer 21 is reduced to 10%, the S / N is reduced, and the focus servo is also unstable. It was a level that did not become.

As another configuration for comparison, when the second information recording layer 22 is also provided with a reflective layer and uses the same detection principle as the first information recording layer 21, the first It goes without saying that no signal from the information recording layer 21 can be obtained at all.

(Example 2)

Next, an example in which the thickness of the reflective film is increased to further increase the amount of light reflected from the first information recording layer 21 will be described. By doing so, the detection from the first information recording layer 21 becomes easier even in the case of a multilayer structure. Here, as shown in FIG. 2, in addition to the second information recording layer 22, a third information recording layer 23 is further provided on the incident surface side, and a total of three information recording layers 21, An optical disk 20 on which 22 and 23 were formed was manufactured, and was used as an optical disk 20 of Example 2.

In Example 2, the thickness of the Ag metal film forming the reflection layer 12 was set to 50 nm. In addition, the second information recording layer 22 and the third information recording layer 23 have the same configuration (material ♦ film thickness) as the second information recording layer 22 of the optical disc 10 of the first embodiment. · An organic dye film with the width of the recording area) was used. Further, in this case, two intermediate layers 13 were formed. At this time, the reflectance of the first information recording layer 21 was 35%.

With respect to the optical disc 20 of Example 2, the amount of light returned from the first information recording layer 21 was observed.

As a result, the amount of return light before recording was 10% of the amount of incident light, and a signal with a modulation factor of 30% was detected.

That is, it was shown that the use of the configuration of Example 2 can achieve a practical level even with an optical disc having three information recording layers.

On the other hand, as a comparison, in the optical disc 20 shown in FIG. 2, the reflective layer 12 made of an Ag metal film was not formed, or the reflective layer 12 had a thickness of 30 nm. When it was only about the extent, the amount of light returned from the first information recording layer 21 was too small to detect and the focus servo was not applied.

Here, the reason why the width of the recording area of the first information recording layer 21 and the width of the recording area of the second information recording layer 22 were set to 0.12 ^ m and 0.16 ^ m in the above embodiment, respectively. A description will be given based on experimental results. Here, we show the results of a similar experiment performed by changing the width of the recording area.

First, the width of the recording area of the second information recording layer 22 is set to 0.06 to 03 00531

Fig. 4A shows the results of measuring the modulation of the reproduction detection signal while changing it within the range of 0.26 m.

When the width of the recording area was set to 0 .Ι δ μ πι, the modulation was 40% as described above, but as shown in Fig. 4 すると, when the width of the recording area was further reduced, the modulation It can be seen that the degree decreases.

This is because, in the reflectivity modulation method, the amplitude of the detection signal simply decreases when the width of the information recording mark decreases, and it is considered that the modulation degree decreases by the decrease in the recording area.

Also, in this reflectivity modulation method, the modulation degree increases as the width of the information recording mark increases, but on the other hand, the crosstalk increases as the width approaches the track pitch. Will not work. In the above embodiment, the track pitch is 0.32 m, so if the width of the information recording mark is 0.25, the crosstalk will be 20 dB (the carrier level of the recording track). And the carrier level of the adjacent track). The degree of modulation is preferably 30% or more empirically in consideration of the ratio to the noise level, and if it is less than 30%, SZN is insufficient and is not practical.

From these facts, it can be seen that in the case of the reflectance modulation method, it is desirable to set the width of the recording area within the range of 0.12 to 0.25 m. Good characteristics can be obtained with a width of 0.16 m of the recording area employed in the above embodiment.

The optimum value of the width P of the recording area differs depending on the diameter of the optical spot. The light spot diameter is a function of the wavelength of the incident light; I and the numerical aperture N A of the objective lens. Assuming that S / N A = α, I = 0.4 in this embodiment.

0 5 μm. N A = 0.85

0. 2 5 «<P <0 .5 2 5 α

It turns out that is preferable. In this formula, all units are m 03 00531 Used.

Incidentally, the light spot of the incident light L has a light distribution with a wide skirt called an airy disk, so that the information recording mark is usually smaller than the light spot. Therefore, when a signal is detected by the reflectance modulation method, the ratio of the reflectance in the information recording mark to the reflectance before recording becomes larger than the modulation degree of the detection signal.

Next, FIG. 4B shows the result of measuring the modulation of the reproduction detection signal while changing the width of the recording area of the first information recording layer 21 in the range of 0.04 to 0.28 m. .

When the width of the recording area was 0.12 ^ m, the modulation factor was 50% as described above, but as shown in Fig. 4B, when the width of the recording area became narrower, the modulation factor decreased. It turns out that it falls.

In addition, the guide groove was formed by exposing the fore-registry with an electron beam in the mastering process. However, if the width was too narrow, the disturbance of the wall surface became conspicuous, resulting in an increase in noise level.

Therefore, even if the degree of modulation was to some extent, the noise level increased and the SZN decreased, so that it was not practical with a recording area width of 0.09 m or less. At 0.22 m, the degree of modulation decreased to about 30%, and the S / N also decreased, which was not practical.

From these facts, it can be seen that when information is reproduced or recorded by the phase modulation method, it is desirable to set the width of the recording area in the range of 0.009111 or more and 0.0 or less. Good characteristics can be obtained with the recording area width of 0.12 ^ m adopted in the above embodiment.

The optimum value of the width P of the recording area in the case of the phase modulation method is λ / Ν Ν = α as a function of the optical wavelength and the numerical aperture NA of the objective lens.

0. 1 9 α; <0 <0. 4 6 α: It turns out that JP03 / 00531 is preferable. In this equation, the unit was ^ m.

4A and 4B that the first information recording layer 21 and the second information recording layer 22 show completely different characteristics depending on the width of the recording area. This is considered to be because the reflectance in the information recording mark after recording is significantly different between the first information recording layer 21 and the second information recording layer 22.

In the above embodiments and examples, the optical recording medium has two or three information recording layers 21, 22, and 23 made of an organic dye and allows light to enter from the side opposite to the substrate 11. Although the present invention is applied to 10, the present invention can be applied to other configurations.

For example, a configuration in which light is incident from the substrate side of an optical recording medium is also possible.In this case, the substrate is made a transparent substrate, and a reflective layer is provided on the opposite side of the information recording layer farthest from the substrate. .

With this configuration, light is incident from the substrate side and the information recording layer is formed.

Compatibility with an optical recording medium having one layer is ensured, and reproduction and recording can be performed on any optical recording medium using the same optical head.

The material of the information recording layer is not limited to the organic dye, and other materials can be used. The type of optical disc is not limited to write-once type

Rewrite type and read only type are also possible.

Furthermore, the shape of the optical recording medium is not limited to a disk as long as a plurality of information recording layers are provided and light can be incident on the plurality of information recording layers.

According to the present invention, the first information recording layer farthest from one main surface, which is a light incident surface, is a phase modulation type information recording layer, regardless of the configuration of the optical recording medium. The recording layer is configured to be a reflectance modulation type information recording layer. The present invention is not limited to the above-described embodiment, and can take various other configurations without departing from the gist of the present invention.

According to the present invention described above, a signal is detected by the phase modulation method for the first information recording layer, and a signal is detected by the reflectance modulation method for the other information recording layers. A signal can be detected with a high degree of modulation.

As a result, good recording / reproducing characteristics can be maintained in a plurality of information recording layers.

Therefore, it is possible to realize a high-density optical recording medium having two or more information recording layers.

In particular, when the reflection layer is provided on the other main surface side of the first information recording layer, the reflectance can be increased by the reflection layer, so that the signal from the first information recording layer can be sufficiently detected. You can do it.

In particular, when the recording film constituting the information recording layer is formed of an organic dye film, the production can be further simplified and the price can be reduced.

Claims

The scope of the claims

An optical recording / reproducing method for reproducing or recording information on at least an optical recording medium,

The optical recording medium has a plurality of information recording layers between one main surface on a light incident side with respect to the optical recording medium and another main surface on the opposite side, and the other main surface. The first information recording layer closest to the optical recording medium is a phase modulation type information recording layer, and the other information recording layer is a reflectance modulation type information recording layer using an optical recording medium.

By the light incident from the one main surface side, information is reproduced or recorded on the first information recording layer by a phase modulation method, and the reflectance modulation is performed on the other information recording layer. Play or record information according to the method

An optical recording / reproducing method characterized by the above-mentioned.

The first information recording layer of the optical recording medium has a reflectance R before recording at a position corresponding to the inside of the information recording mark. When the reflectance after recording at the same position is R, the rate of change is (R.1R) / R0 force, which is smaller than the modulation degree of the reproduction detection signal of the information recording mark. Is the same rate of change of the information recording mark (R.I.R) ZR. 2. The optical recording / reproducing method according to claim 1, wherein the optical recording / reproducing method has a modulation degree equal to or higher than a modulation degree of a reproduction detection signal of the information recording mark.

A main surface through which light can enter, and a plurality of information recording layers between the one main surface and the other main surface on the opposite side,

The first information recording layer closest to the other main surface is a phase modulation type information recording layer,

Other information recording layer was changed to reflectivity modulation type information recording layer

An optical recording medium characterized by the above-mentioned.

. The width of the recording area of the reflectance modulation type information recording layer is 4. The optical recording medium according to claim 3, wherein the width of the modulation type information recording layer is wider than the width of the recording area.

5. In the first information recording layer, the reflectance before recording at a position corresponding to the information recording mark is R. Where R is the reflectivity after recording at the same position and R is the rate of change (R-one R) / R. Is smaller than the modulation degree of the reproduction detection signal of the information recording mark, and the other information recording layer has the same change rate (R _D -R) R 0 of the information recording mark as the information recording mark. 4. The optical recording medium according to claim 3, wherein a modulation degree of the reproduction detection signal is set to be equal to or more than the modulation degree.

6. A method according to claim 3, wherein at least one or more of the plurality of information recording layers is formed of a recording film whose optical constant changes due to light absorption. Optical recording medium according to the item.

7. The optical recording medium according to claim 6, wherein the recording film contains an organic material that causes a change in optical constants due to a change in physical properties due to light absorption.

8. The optical recording medium according to claim 7, wherein an organic dye is used as the organic material.

9. The optical recording medium according to claim 3, wherein a reflection layer is provided on the other main surface side of the first information recording layer.